Programming

 
$ gcc sem.c -o sem -lpthread
Undefined                       first referenced
 symbol                             in file
sem_init                            /var/tmp//ccAGJZdT.o
sem_post                            /var/tmp//ccAGJZdT.o
sem_wait                            /var/tmp//ccAGJZdT.o
ld: fatal: Symbol referencing errors. No output written to sem
collect2: ld returned 1 exit status

$ gcc sem.c -o sem
Undefined first referenced
symbol in file
sem_init /var/tmp//cc3WmF9R.o
sem_post /var/tmp//cc3WmF9R.o
sem_wait /var/tmp//cc3WmF9R.o
ld: fatal: Symbol referencing errors. No output written to sem
collect2: ld returned 1 exit status
$

 
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <pthread.h>
#include <semaphore.h>
#include <sys/sem.h>
#define MAX_THREAD 100
typedef struct
{
    int start,end;
} param;
sem_t mysem;
void *count(void *arg)
{
    sem_wait(&mysem);
    int i =0;
    param *p=(param *)arg;
    printf("\nprintfrom %d  to  %d\n",p->start,p->end);
    for(i =p->start ; i< p->end ; i++)
    {
        printf(" i = %d",i);sleep(1);
    }
    sem_post(&mysem);
    return (void*)(1);
}
int main(int argc, char *argv[])
{
    if (sem_init(&mysem,0,1))
    {
    perror("init");
    }
    int n,i;
    pthread_t *threads;
    param *p;
    if (argc != 2)
    {
        printf ("Usage: %s n\n",argv[0]);
        printf ("\twhere n is no. of threads\n");
        exit(1);
    }
    n=atoi(argv[1]);
    if ((n < 1) || (n > MAX_THREAD))
    {
        printf ("arg[1] should be 1 - %d.\n",MAX_THREAD);
        exit(1);
    }
    threads=(pthread_t *)malloc(n*sizeof(*threads));
    p=(param *)malloc(sizeof(param)*n); /* Assign args to a struct and start thread */
    for (i=0; i<n; i++)
    {
        p[i].start=i*100;
        p[i].end=(i+1)*100;
        pthread_create(&threads[i],NULL,count,(void *)(p+i));
    }
    printf("\nWait threads\n");
    sleep(1); /* Wait for all threads. */
    int *x = malloc(sizeof(int));
    for (i=0; i<n; i++)
    {
        pthread_join(threads[i],(void*)x);
    }
        free(p);
        exit(0);
return 0;
}

gcc sem.c -o sem -lrt